Neural correlates of illusory motion perception in the Pinna-figure

Abstract

We investigated the recently discovered Pinna-Illusion using the fMRI technique. The original figure investigated by Pinna and Brelstaff (2000), which induces the illusion of rotatory motion, consists of two concentric rings of circular arranged micro patterns bounded in a specific way by light and dark lines. The illusion of rotatory motion occurs whenever this class of flat static patterns are moved across the peripheral visual field during an observer's own movement towards or away from the figure. To create the illusion suitable for the MR scanner a simulation of the subject's self-movement was created by a computerised animation. The animation generated contraction and expansion of the concentric circles on the retina i.e. outward and inward radial flow. In a block design we compared the rotatory motion illusion with two controls and one baseline condition, which all did not show the effect of the illusion, when animated. 10 volunteers, participants with normal or corrected to normal vision were tested. Statistical analysis of data acquired in this study was carried out with SPM2 using t-tests. Two bilateral occipito-temporal activation sites, and a unilateral activation in the frontal lobe were revealed to be more activated during the motion illusion in comparison to the non illusory visual stimulation (P < 0.05, FDR). The bilateral occipito-temporal activation was found to be adjacent to the V5 area, probably within the V5 complex and LOC and corresponds partly to the activation found in a PET study, which investigated the rotatory motion illusion in a static figure called Enigma (Zeki et al., 1993). Our results might challenge the view, which considers illusory motion to be detected by the same visual channels as real motion. We propose further psychophysical and brain imaging investigations and experimental improvements in order to gain insight into the general perceptual mechanisms of illusory motion.